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# shell problem

#### Israr

##### Active member
I need to shell a box of 286x150x8200 mm dimensions with 3 mm thickness. It fails. Please help.

Israr

G

#### Guest

##### Guest
Adjust your relative accuracy. Setup > Accuracy. Lower the number. The default is .0012. Try .0008, .0004, etc.

##### Moderator
The longest diagonal on your part is 8206mm and the shortest is going to be 3mm.

Using PTC's formula A < F * s / d (see link below)

for acerage model (see link below):

A = accuracy setting

F = ~3 for average models (1=really complex, 10=flat plate)

s = 8206 (longest diagonal measurement)

d = 3

3 * 3 / 8206 = 0.001096758

So your relative accuracy setting should be set less than (more precise than) 0.00109. Since the default setting is .0012, Pro/E can not calculate your geometry precidely enough to get those really small dimensions.

http://www.ptc.com/cs/tpi/32869.htm

Excerpt:

To illustrate the meaning of this equation, consider the following example: With a part in the shape of a sheetmetal plate which has a largest diagonal 10 inches long and has accuracy set to the default 0.0012, the smallest edge which is still discernible is about 1/10 * 0.0012 * 10.0 in. = .0012 inch. If the part accuracy is changed to 0.0001, the smallest edge can be about .0001 in. If the largest part diagonal is 1 inch and accuracy is default, then the smallest edge can be about 0.00012 in. With more complicated geometry, these values

represent the lower bound of what distances can be discerned on the model. In general, the smallest distances would be about 3 times these values. Keep in mind that this smallest distance changes as features are added due to the change in the part diagonal.

#### Israr

##### Active member
Thank Brian,

You really helped me.

Israr